Effects of biological fertilizers application and various amounts of urea fertilizers under water stress conditions on yield, nitrogen use efficiency and effective ingredients of Calendula officinalis L.

In order to investigate the effects of biological fertilizers application and various amounts of urea fertilizers under the water stress conditions on yield, nitrogen use efficiency, and effective ingredients of Calendula officinalis L., an experiment was implemented during the two cultivation years of 2015-2106 and 2016-2017. The study was conducted at the research farm of Islamic Azad University, Varamin-Pishva Branch. The experiment was performed in three replications as a split-split plot in a completely randomized blocks design. The experimental treatments included two levels of water stress as (the main factor): the absence of water stress (control) and irrigation cut off at the budding stage, as well as, four levels of biological fertilizers (as sub-factor) (no use), the application of Azotobacter (Chroococum), the application of Azospirillum (Brasilense), and combined application of Azotobacter and Azospirillum. Urea fertilizer sources were also classified (sub-factor) in four levels including no use (control), recommended amount of sulfur coated urea fertilizer (175 kg/ha of recommended amount of fertilizer), 75% of recommended amount of sulfur coated urea fertilizer (131 kg/ha), and the recommended amount of urea fertilizer without coating at 175 kg/ha. The results showed that irrigation cut off at budding stage resulted in reduced flower yield, biological yield, the amount of nitrogen, nitrogen use efficiency (crop efficiency), and nitrogen uptake efficiency. However, it resulted in the increased nitrogen use efficiency, α-cadinol, and morolol. In addition, in both years of experiment, the combined use of Azotobacter and Azospirillum, along with the recommended amount of sulfur coated urea fertilizer resulted in the increased content of α-cadinol. The highest nitrogen use efficiency was achieved under non-water stress conditions and the combined use of bio-fertilizer (Azotobacter and Azospirillum) and the use of 75% of the recommended amount of sulfur coated urea fertilizer. In the second year, the lack of water stress and the combined use of bio-fertilizer (Azotobacter and Azospirillum) and the recommended amount of sulfur coated urea fertilizer also resulted in a significant reduction in nitrogen use efficiency. In the first and second years, the lack of water stress and the combined use of Azotobacter and Azospirillum and the recommended amount of sulfur coated urea fertilizer resulted in increased flower yield and biological yield.